This invention relates to a phosphor and a method for producing the same.
It is known in the art that a GaN monocrystal exhibits a blue or green luminous color increased in luminance when it is used for an LED, an LD or the like. In the past, excitation of the material by electron beams for luminescence was attempted. However, the prior art fails to practically realize techniques of forming GaN into a phosphor in the form of a powder.
A failure in realizing practical production of such a powdery GaN phosphor which emit light due to excitation by electron beams is due to the fact that it is highly difficult to nitride the GaN phosphor unlike other phosphors. More particularly, the GaN material is reduced in difference between a nitriding temperature thereof (900 to 1050xc2x0 C.) and a temperature at which decomposition thereof is started, so that heating of the material or phosphor under normal conditions causes nitriding of the phosphor and decomposition thereof to tend to be concurrently carried out, resulting in a lot of defects occurring in the phosphor. Such defects deteriorate a light emitting or luminous mechanism of the phosphor, to thereby fail to permit the phosphor to exhibit satisfactory luminance.
Synthesis of GaN used for an LED or the like is normally carried out in a manner to instantaneously cool GaN concurrently with formation of GaN by a reaction of starting materials, to thereby deposit it on a sapphire substrate. This is a reaction under thermal non-equilibrium conditions, so that only synthesis of GaN by nitriding is proceeded while preventing decomposition of the material produced. However, a phosphor used for a luminous section of a fluorescent display device must be formed into a display pattern of any desired configuration, so that the phosphor is required to take the form of a powder. For example, any conventional pattern formation techniques such as printing, slurry techniques, deposition, precipitation or the like are carried out using a phosphor in the form of a powder.
The present invention has been made in view of the foregoing situation of the prior art.
Accordingly, it is an object of the present invention to provide a phosphor in the form of a powder which is formed on at least a part of a surface thereof with a compound semiconductor made of elements of Groups IIIA-VA of the periodic table (hereinafter also referred to as xe2x80x9ccompound semiconductor of Groups IIIA-VAxe2x80x9d) in the form of either fine particles or a thin film, as represented by a GaN phosphor.
It is another object of the present invention to provide a method for producing a phosphor which is capable of providing such a phosphor as described above.
In accordance with one aspect of the present invention a phosphor is provided. The phosphor includes a carrier particle and a compound semiconductor deposited in the form of fine particles or a thin film on a surface of the carrier particle by hetero-epitaxial growth. The compound semiconductor is made of elements of Groups IIIA-VA of the periodic table.
In a preferred embodiment of the present invention, the phosphor is excited by ultraviolet rays or electron beams.
In a preferred embodiment of the present invention, each of the fine particles or the thin film has a dopant added thereto.
In a preferred embodiment of the present invention, the dopant comprises at least one element selected from the group consisting of Zn, Si and Mg.
In a preferred embodiment of the present invention, the compound semiconductor is selected from the group consisting of GaxIn1xe2x88x92xN (0 less than xxe2x89xa61) and GaxIn1xe2x88x92xP (0 less than xxe2x89xa61).
In a preferred embodiment of the present invention, the carrier particle is made of a material selected from the group consisting of nitrides and oxides of Si and Al, and a mixture thereof.
In a preferred embodiment of the present invention, the carrier particle is made of a material selected from the group consisting of AlN and Al2O3.
In a preferred embodiment of the present invention, the carrier particle has a particle diameter within a range between 0.01 xcexcm and 2 xcexcm.
In accordance with another aspect of the present invention, a method for producing a phosphor is provided. The method includes the step of subjecting fine particles of a compound semiconductor or a thin film thereof to hetero-epitaxial growth on a surface of a carrier particle, wherein the compound semiconductor is made of elements of Groups IIIA-VA of the periodic table.
In a preferred embodiment of the present invention, the method further includes the step of imparting energy to the carrier particle while or after introducing organic metal gas into a closed space in which the carrier particle is received, to thereby form the thin film on the surface of the carrier particle by chemical vapor deposition.
In a preferred embodiment of the present invention, ammonia gas and dopant-ingredient containing gas are introduced into the closed space together with the organic metal gas.
In a preferred embodiment of the present invention, the organic metal gas is selected from the group consisting of TMGa and TMIn, the dopant-ingredient containing gas is selected from the group consisting of DMZn, DEZn and SiH4, and the carrier particle is selected from the group consisting of AlN and Al2O3.
In a preferred embodiment of the present invention the carrier particle is AlN and is removed by subjecting the carrier particle to a wet or dry etching treatment after formation of the fine particles or thin film, resulting in only the compound semiconductor being obtained.